1. Technical Field of the Invention
This invention relates to a multi-color gravure press, and more particularly to the arrangement of printing drums thereof.
2. Related Art
A conventional multi-color press 71 will be described in reference to FIG. 1. The multi-color press 71 performs printing as described below by means of a first unit 10 and a second unit 20.
First, a paper sheet 34 is fed by a feeder section 73 to an impression cylinder 72. In the first unit 10, a plate cylinder 14 has a metallic gravure plate 13 wound thereon so that ink stored in an ink pan 18 adheres to the surface of the gravure plate 13 as an ink roller 16 rotates. This causes a concave pattern formed on the gravure plate 13 to be filled with ink. Surplus ink adhering to the surface of the gravure plate 13 is scraped off by a doctor blade 17.
Printing onto the paper sheet 34 fed to the impression cylinder 72 is performed one by one with ink stored in the concave pattern of the gravure plate 13 at the nearest point between the impression cylinder 72 and the first plate cylinder 14.
In the second unit too, printing in a different color is performed in a similar manner. In order to compensate phase difference between printing surfaces of the first and second units, the gravure plates are wound with a phase difference from each other corresponding to the phase difference described above.
When printing in the second unit is over, the printed paper sheet 37 is removed from the impression cylinder 72, transferred through a delivery roller 41, a delivery chain 39 and a delivery roller 42, and stacked in a delivery section.
The conventional gravure press 71 as described above, however, has disadvantages as described below.
With the multi-color gravure press using plastic material for the gravure plates, it is possible that damages are caused on the surfaces of the gravure plates. The cause of such damages is as follows: As already described above, in order to compensate the phase difference between the printing surfaces of the first and second units, the gravure plates are wound on the plate cylinders with a phase difference from each other corresponding to the phase difference between the printing surfaces. As a result, when it is arranged that the doctor blade of the first unit does not stop on the printing surface of the gravure plate of the first unit, it is possible that the doctor blade of the second unit stops on the printing surface of the gravure plate of the second unit.
Another disadvantage is as follows: The distance between the point at which the doctor blade is in contact with the gravure plate and the nearest point between the plate cylinder and impression cylinder for one unit is different from the distance for the other unit. This causes difference in drying conditions of ink and it becomes difficult to obtain printed paper sheets of an identical quality. In particular, when the distance described above is large, the state of ink filling the concave pattern of the gravure plate is likely to change, and therefore the printing conditions become unstable and result in scatter in quality of the printed paper sheets.